1. Field of the Invention
The present invention relates to a wireless communication apparatus and a wireless communication, and a computer program with which packets in compliance with a predetermined standard format are received and processed. In particular, the invention relates to a wireless communication apparatus and a wireless communication, and a computer program with which packets in multiple formats in which two or more different types of preamble information and intra-header control information are multiplexed are received and processed.
2. Description of the Related Art
A wireless network draws attention as a system for freeing a wiring in a traditional wired communication system. As a standard specification related to the wireless network, IEEE (The Institute of Electrical and Electronics Engineers) 802.11 or IEEE 802.15 can be exemplified. For example, in IEEE 802.11a/g, as a standard specification related to a wireless LAN, an OFDM (Orthogonal Frequency Division Multiplexing) modulation system which is one of multi carrier systems is adopted.
In the wireless communication, in general, a preamble made of a repetition of sequences is prepended at the beginning of packets, and on a receiver side, the preamble is used to find the packets and perform a synchronization processing. Also, when the synchronization acquisition is ended in the preamble part, subsequent control information (SIGNAL field) in a header is decoded to obtain information used for data decoding such as a packet length, a modulation system, and an encoding system. Then, if the reception packets are addressed to its own station, the decoding processing is continuously performed over the relevant packets. If the reception packets are not addressed to its own station, an end time of the relevant packets is measured, and a sending operation stands by, so that mutual signal interference is avoided.
In addition, the specification of IEEE 802.11a/g supports a modulation system of achieving a maximum communication system of 54 Mbps, but a next generation wireless LAN specification for realizing a further higher bit rates is demanded. For example, as an expansion specification of IEEE 802.11, IEEE 802.11n adopting an OFDM_MIMO (Multiple Input Multiple Output) communication system is specified.
In a technological trend in which succeeding specifications are continuously established in this way, a communication environment is anticipated where packets in two or more different types of packet formats are transmitted on the same channel.
In such a communication environment, a wireless terminal in compliance with a succeeding specification is requested to have a compatibility with packet formats in compliance with older (legacy) specifications. For example, IEEE 802.11n allows a coexistence with a legacy terminal, but in order to solve a problem that the legacy terminal does not decode a MAC frame part transmitted in a high speed HT (High Throughput) part, that is, a Duration field in the MAC header is not interpreted and NAV is not properly set, a spoofing (“masquerade” or “impersonation”) technology is applied in which a Rate field and a LENGTH field in a PHY header which can be decoded also by the legacy terminal is used to carry Duration information (for example, see Japanese Unexamined Patent Application Publication No. 2006-50526, paragraphs 0066 to 0068).
Also, in an environment where wireless communication apparatuses of various systems which use the same frequency band exist in a mixed manner, a wireless communication apparatus has been proposed which avoids an unwanted deterioration in a communication speed performance and maintains a fairness in speeds between the wireless communication apparatuses (for example, see Japanese Unexamined Patent Application Publication No. 2002-300172).
Furthermore, also while avoiding the channel congestion, in order to operation the network efficiently, the respective wireless terminals should correctly measure the sending end time of the reception packets from preamble information and intra-header control information in two or more different types of packet formats.
However, measurement means capable of coping with all modulation system and coding system indicated by the SIGNAL information including a packet transmission mode which is not supported by its own terminal should be prepared, and there is a problem that the mounting becomes complex, or the circuit scale is increased.